1. Field of the Invention
This invention relates to housings for loudspeaker systems having foam particularly affixed to interior walls of the housing to increase wall stiffness and provide sound damping.
2. Related Art
A loudspeaker typically is a device that converts electrical energy into audible sound. The loudspeaker usually consists of a thin flexible sheet called a diaphragm that moves in response to an electric signal from an amplifier. The diaphragm, the amplifier, and other driver components of the loudspeaker typically are housed in some sort of speaker enclosure. One of the more common types of enclosure is a sealed enclosure, also known as an acoustic suspension cabinet. Acoustic suspension cabinets generally are designed to be completely sealed, so that no air may escape.
In operation, electric signals from the amplifier vibrate the diaphragm. The vibrations create sound waves in the air around the loudspeaker. For example, forward sound waves travel outward into free airspace, while backward sound waves travel into an enclosure. Quality speaker systems typically have sound damping features that prevent noise inside the enclosure from passing outside.
For acoustic suspension cabinets, the internal air pressure of the cabinet is constantly changing during the operation of the loudspeaker. When the diaphragm moves in, the internal air pressure typically is increased and when the diaphragm moves out, the internal air pressure typically is decreased. In other words, the movement of the diaphragm may alternately increase and decrease the pressure level within the cabinet. An efficient speaker system is able to account for the change in pressure in the sealed enclosure to maintain the sound power level.
Some conventional loudspeaker enclosures are designed utilizing wood cabinets that provide stiff, sound damping walls. However, wood typically is prohibitively expensive to manipulate into structural shapes that house certain speaker configurations or ornamental shapes that are pleasing to a consumer-driven market. In addition, in many applications, wood cabinets take too long to produce and cannot be utilized in high volume production.
By way of comparison, plastic provides cabinet designers with the freedom to house a multitude of speaker configurations as well as create consumer-driven ornamental shapes. In addition, manufacturers may rapidly produce plastic cabinets, making them ideal for high volume production runs. Thus, many modern speaker cabinets are made of plastic.
Although the utilization of plastic for speaker cabinets typically is superior in industrial design over wood, the utilization of plastic for speaker cabinets gives rise to wall flex and sound damping problems. For example, certain speaker configurations require plastic cabinet walls having multiple inches. However, molding cycle time and process yield problems require that the thickness of these plastic walls not exceed 0.187 to 0.250 inches. The result is a long, thin expanse of plastic.
A long, thin expanse of plastic potentially creates a large, weak surface that may flex in and out in,along with the diaphragm. As the cabinet walls flex in and out, they alter the interior volume of the sealed cabinet away and result in differing pressures within the interior. The driver typically will draw more current and work harder to counter the harmonic energy of the wall movements to maintain the desired sound power level. However, as the wall becomes stiffer, the driver requires less current to compensate for wall movement to make the overall system more efficient. Thus, it is desirable to minimize the movement of the plastic walls. Here, increasing the flexural rigidity of the plastic walls decreases their ability to move.
Injected molded plastic ribs have been utilized in the past to make plastic cabinet walls more rigid. Unfortunately, larger plastic walls require large, thick ribs. If the plastic ribs are too thick, then the thick ribs create undesirable sink marks on the exterior of the cabinet. Additionally, ribs alone will not provide the sound damping needed in a quality speaker system. Therefore, there is a need to stiffen the walls of a loudspeaker plastic enclosure while damping sounds internally generated within the plastic enclosure.